Contact Edge Research Articles

A Comprehensive Optimization Model of Tooth Surface Parameters for the Minimization of Contact Stress of Helical Face Gears by Considering the Avoidance of Edge Contact

Optimization with edge contact avoidance and contact stress minimization is essential for gear design. Due to the complex geometry of modified helical face gear drives, it is complicated to find the optimal design parameters with the consideration of issues including loading, assembly errors, and edge contact. As the finite element method is tedious and time-consuming, an optimization model with a simplified algorithm of the loaded tooth contact analysis with errors (ELTCA) for modified helical face gears is presented, and it can programmatically optimize the contact stress with edge contact avoidance. Firstly, a simplified ETCA algorithm is introduced, which reduces the five unknowns in the traditional contact equations to three. Secondly, the LTCA is analytically implemented according to the Hertz theory. Subsequently, an optimization model with the objective function of avoiding edge contact and reducing maximum contact stress is proposed. Furthermore, the proposed model is applied to reveal the effects of design parameters and assembly errors on the optimized contact path and stress. The results show that the optimization model is accurate and efficient; the design parameters and assembly errors have great effects on the meshing of modified helical face gears.

Recent Progress in 1D Contacts for 2D-Material-Based Devices.

Recent studies have intensively examined 2D materials (2DMs) as promising materials for use in future quantum devices due to their atomic thinness. However, a major limitation occurs when 2DMs are in contact with metals: a van der Waals (vdW) gap is generated at the 2DM-metal interfaces, which induces metal-induced gap states that are responsible for an uncontrollable Schottky barrier (SB), Fermi-level pinning (FLP), and high contact resistance (RC ), thereby substantially lowering the electronic mobility of 2DM-based devices. Here, vdW-gap-free 1D edge contact is reviewed for use in 2D devices with substantially suppressed carrier scattering of 2DMs with hexagonal boron nitride (hBN) encapsulation. The 1D contact further enables uniform carrier transport across multilayered 2DM channels, high-density transistor integration independent of scaling, and the fabrication of double-gate transistors suitable for demonstrating unique quantum phenomena of 2DMs. The existing 1D contact methods are reviewed first. As a promising technology toward the large-scale production of 2D devices, seamless lateral contacts are reviewed in detail. The electronic, optoelectronic, and quantum devices developed via 1D contacts are subsequently discussed. Finally, the challenges regarding the reliability of 1D contacts are addressed, followed by an outlook of 1D contact methods.

ELUCID. VII. Using Constrained Hydro Simulations to Explore the Gas Component of the Cosmic Web

Using reconstructed initial conditions in the Sloan Digital Sky Survey (SDSS) survey volume, we carry out constrained hydrodynamic simulations in three regions representing different types of the cosmic web: the Coma cluster of galaxies; the SDSS Great Wall; and a large low-density region at z ∼ 0.05. These simulations, which include star formation and stellar feedback but no active galactic nucleus formation and feedback, are used to investigate the properties and evolution of intergalactic and intracluster media. About half of the warm-hot intergalactic gas is associated with filaments in the local cosmic web. Gas in the outskirts of massive filaments and halos can be heated significantly by accretion shocks generated by mergers of filaments and halos, respectively, and there is a tight correlation between the gas temperature and the strength of the local tidal field. The simulations also predict some discontinuities associated with shock fronts and contact edges, which can be tested using observations of the thermal Sunyaev–Zel’dovich effect and X-rays. A large fraction of the sky is covered by Lyα and O vi absorption systems, and most of the O vi systems and low-column-density H i systems are associated with filaments in the cosmic web. The constrained simulations, which follow the formation and heating history of the observed cosmic web, provide an important avenue to interpret observational data. With full information about the origin and location of the cosmic gas to be observed, such simulations can also be used to develop observational strategies.

Musculoskeletal multibody dynamics investigation of posterior-stabilized total knee prosthesis

Posterior-stabilized total knee prostheses have been widely used in orthopedic clinical treatment of knee osteoarthritis, but the patients and surgeons are still troubled by the complications, for example severe wear and fracture of the post, as well as prosthetic loosening. Understanding the in vivo biomechanics of knee prostheses will aid in the decrease of postoperative prosthetic revision and patient dissatisfaction. Therefore, six different designs of posterior-stabilized total knee prostheses were used to establish the musculoskeletal multibody dynamics models of total knee arthroplasty respectively, and the biomechanical differences of six posterior-stabilized total knee prostheses were investigated under three simulated physiological activities: walking, right turn and squatting. The results showed that the post contact forces of PFC Sigma and Scorpio NGR prostheses were larger during walking, turning right, and squatting, which may increase the risk of the fracture and wear as well as the early loosening. The post design of Gemini SL prosthesis was more conductive to the knee internal-external rotation and avoided the edge contact and wear. The lower conformity design in sagittal plane and the later post-cam engagement resulted in the larger anterior-posterior translation. This study provides a theoretical support for guiding surgeon selection, improving posterior-stabilized prosthetic design and reducing the prosthetic failure.

Improved rectification characteristics of the GR/Blue P/GR selector by doping: First-principles study

In this paper, a graphene (GR)/monolayer (ML) blue phosphorous (Blue P)/GR selector was studied based on the first-principles theory. Due to different contact edges, four GR–Blue P lateral heterojunctions were constructed, namely, armchair–armchair (A–A), zigzag–armchair (Z–A), armchair–zigzag (A–Z), and zigzag–zigzag (Z–Z). As demonstrated by the binding energy and Mulliken population, we found that the Z–Z heterojunction was relatively stable. Furthermore, a GR/Blue P/GR selector based on the Z–Z heterojunction interface was proposed with a nonlinear (NL) coefficient is 105. However, the drive current of this device was insufficient. A P atom of the resistive layer was separately substituted with four different atoms (Ni, Cu, N, and Cl) to effectively improve selector performance. The energy band structure was half-metallic when doped with Ni or Cu while the others still maintained semiconductor characteristics, and the bandgap was significantly reduced. The Schottky barrier height and width of the interface (GR–Blue P), with Cl as the substituted impurity, were the smallest, leading to a three order of magnitude increase in the NL coefficient. The calculation shows that GR/Blue P/GR devices can be integrated as selectors in Resistive switching Random Access Memory (RRAM) arrays. This work also has a certain guiding significance for manufacturing new types of two-dimensional lateral selector apparatuses.

Atomic transistors based on seamless lateral metal-semiconductor junctions with a sub-1-nm transfer length

The edge-to-edge connected metal-semiconductor junction (MSJ) for two-dimensional (2D) transistors has the potential to reduce the contact length while improving the performance of the devices. However, typical 2D materials are thermally and chemically unstable, which impedes the reproducible achievement of high-quality edge contacts. Here we present a scalable synthetic strategy to fabricate low-resistance edge contacts to atomic transistors using a thermally stable 2D metal, PtTe2. The use of PtTe2 as an epitaxial template enables the lateral growth of monolayer MoS2 to achieve a PtTe2-MoS2 MSJ with the thinnest possible, seamless atomic interface. The synthesized lateral heterojunction enables the reduced dimensions of Schottky barriers and enhanced carrier injection compared to counterparts composed of a vertical 3D metal contact. Furthermore, facile position-selected growth of PtTe2-MoS2 MSJ arrays using conventional lithography can facilitate the design of device layouts with high processability, while providing low contact resistivity and ultrashort transfer length on wafer scales.

The cohesive zone crack analogue for fretting fatigue based on mild wear

Fretting fatigue is an important problem that plagues many mechanical components that are in contact under vibrational loading. Life assessment of fretting fatigue cracking is important, with the damage initiation being difficult to estimate. This work extends a well-known fretting fatigue model, the crack analogue model that examines fretting induced by complete contacts or by adhering incomplete contacts of metallic surfaces. This is done by introducing cohesive zones at the contact edges. These zones address several issues related to friction and wear, by combining them in the case of mild wear where asperity plastic shearing is the dominant inelastic mechanism. Thus, the micromechanical behaviour of the surface topology is naturally introduced into the analysis. The surface roughness becomes an internal variable that evolves with the cyclic loading. The work of friction dissipates the mechanical energy and at the same time becomes the precursor of large scale wear. A predictive methodology for fretting crack nucleation is proposed through a novel cohesive model that incorporates friction and mild wear, lifting much pathology encountered by simple friction models at high normal loads.

Top-Rem grinding tool modification considering loaded edge contact for spiral bevel gears

Focusing on the collaborative manufacturing requiring meshing interface physical performances, an innovative Top-Rem grinding tool modification considering loaded edge contact is proposed for spiral bevel gears. Accurate Top-Rem grinding tool parameters can instead of machine-tool settings and their impact in the sophisticated flank topography correction technique. At first, the whole Top-Rem tool modification includes: i) arc-shaped blade part; ii) Top-Rem part; iii) top fillet part. Then, grinding tool modification model considering both loaded contact and geometric accuracy is established. Where, three important constraint conditions were taken into accounts: i) geometric boundary considering loaded edge contact, ii) root overcutting, and iii) flank geometric accuracy. Moreover, two kinds of optimization strategies are proposed to improve the accuracy and efficiency of the whole modification: i) two types of modification by the different tool modification parameters; ii) sensitivity analysis with respect to ease-off for optimization operation of the unknown variables. Finally, the given instances can verify that it can get accurate and effective loaded contact performance optimization in early stage of full life cycle product development.

Investigation of plastic and slipping regions at the edge of an adhered complete contact of elastically dissimilar materials

Slipping and yielding at a sharp edge in an adhered and complete contact problem is studied. Eigenvalue problem is formed and eigen-solutions are obtained. Stress distribution in the vicinity of the sharp edge is analyzed using the singular terms of the stress equations. Generalized stress intensity factors, KI and KII are evaluated using a simple finite element analysis. Von Mises yield criterion is applied to observe the boundary of the plastic region on the contact surface. Ratio of the shear to normal stresses is compared with the coefficient of friction to estimate the slip region. With using those analysis method, analyzed is a contact between a cracked pellet and a cladding tube of a nuclear fuel rod, made of uranium dioxide and zirconium alloy, respectively, as an example problem. Under the average contact stress of 10 MPa, the contact length of 10 mm, and 0.3 ≤ μ ≤ 0.7, the size of the plastic region is found extremely tiny (order of 10-6 mm) in the cladding tube. Whereas, the size of the slip region in the vicinity of the contact edge dramatically changes (order of 1.0 ∼ 10-8 mm). The effect of material dissimilarity is investigated for the condition of xp = xs. The result is displayed in the Dundurs parallelogram domain, (α,β).

(Invited) Influence of Materials and Processing on Edge Contacts to 2D Semiconductors

The most common approach for establishing electrical contacts to 2D semiconductors, such as MoS2, is by fabricating metal contacts on top of the inert crystal surface. From an electron transport perspective, these top-contact interfaces can be awkward, with a van der Waals gap or some difficult-to-control form of interfacial bonding. Pure edge contacts (where the interface between the metal and 2D semiconductor occurs completely along the open bonds of the 2D crystal edge) provide a more natural bonding structure and potentially better carrier transport behavior; however, edge contacts have proven more difficult to realize. In this talk, recent success with establishing clean, pure edge contacts between metals and 2D semiconductors will be discussed, including an approach involving an in situ ion beam within a thin-film deposition system. Evaluation of these edge contacts compared to other approaches will be provided, along with demonstration of how edge-contact scaling affects the performance of 2D transistors compared to top-contact scaling. While there remains much to be learned about these interesting metal-2D edge interfaces, results thus far show significant promise for yielding a more scalable and potentially reproducible contact for 2D-based devices.

Evaluation of polyvinyl chloride adhesion to 2D crystal flakes

We investigated the adhesion of polyvinyl chloride (PVC) to 2D crystal flakes on SiO2/Si substrates. Although the anchoring effect cannot be used to explain adhesion to atomically flat surfaces, PVC is sufficiently strongly adhesive to 2D crystal flake surfaces to allow pickup from SiO2/Si substrates via surface contact alone. Results of the pickup test, whether pickup is possible or impossible, were plotted on a map of contact surface area ratio vs. contact edge length ratio, which allowed us to identify the conditions under which flakes can be picked up using PVC and to discuss the adhesion strengths of the surface and edge. This study provides a method for the evaluation of adhesion forces between polymers and 2D flakes and demonstrates that PVC is a useful polymer for deterministic transfer and versatile manipulation of 2D flakes.

Effects of surface stress on the indentation response of an elastic half-space

Nanoindentation technique, which is based on Hertzian contact theory and Sneddon's solutions for the contact between a rigid indenter and an elastic half-space, has been widely investigated due to its practical importance in localized mechanical test of submicron structures. However, both the Hertzian contact theory and Sneddon's solutions do not take into account the contribution of surface stress to contact deformation. In this work, we study the effect of surface stress without the out-of-plane term on the indentation deformation of an elastic half-space by rigid, axisymmetric indenters, including flat-ended cylindrical, conical and spherical indenters. In contrast to classical theories, which are based on physically admissible condition of finite normal stress at contact edge, an alternative condition of geometrical continuity at contact edge is used to determine the contact radius. The numerical results reveal the combinational effects of the surface stress and Poisson's ratio on the load-displacement relationship for the indentation of the elastic half-space. The surface stress causes significant change in shear stress and modest variation in normal stress in the direction normal to the surface of the elastic half-space. The numerical method used in this work offers a feasible approach to study the effect of surface stress on the contact deformation of elastic substrates.

Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks

Abstract Concrete cracks in structures such as water tanks and nuclear power stations cause anxiety to owners, contractors and engineers. These cracks may significantly increase the structure’s permeability and thus increase leakage, reduce durability, and eventually lead to loss of structural functionality. Therefore it is important to minimize their occurrence and size. To identify effective ways of minimizing cracking in young concrete segments, a parametric study was conducted using the finite element method (FEM). Parameters considered include casting sequence, joint position, wall height, and cooling. The study examined continuous and jumped casting approaches to the casting of a cylindrical reinforced concrete tank for a sewage-treatment plant, with and without the application of the ‘kicker’ technique in which the lower part of the wall is cast with the slab. The main cause of cracking is thermal change and restraint imposed by adjacent older structures, and the FEM predictions agree well with experimental observations. Continuous casting is most effective at minimizing cracking because it creates only two contact edges between newly cast and existing structures producing the lowest level of restraint. The kicker technique is shown to be very effective for reducing restraint and consider rephasing.

Comparison of joint load, motions and contact stress and bone‐implant interface micromotion of three implant designs for total ankle arthroplasty

Background and ObjectiveLoosening and wear are still the main problems for the failure of total ankle arthroplasty, which are closely related to the micromotion at the bone-implant interface and the contact stress and joint motions at the articular surfaces. Implant design is a key factor to influence the ankle force, motions, contact stress, and bone-implant interface micromotion. The purpose of this study is to evaluate the differences in these parameters of INBONE II, INFINITY, and a new anatomic ankle implant under the physiological walking gait of three patients. MethodsThis was achieved by using an in-silico simulation framework combining patient-specific musculoskeletal multibody dynamics and finite element analysis. Each implant was implanted into the musculoskeletal multibody dynamics model, respectively, which was driven by the gait data to calculate ankle forces and motions. These were then used as the boundary conditions for the finite element model, and the contact stress and the bone-implant interface micromotions were calculated. ResultsThe total ankle contact forces were not significantly affected by articular surface geometries of ankle implants. The range of motion of the ankle joint implanted with INFINITY was a little larger than that with INBONE II. The anatomic ankle implant design produced a greater range of motion than INBONE II, especially the internal-external rotation. The fixation design of INFINITY achieved lower bone-implant interface micromotion compared with INBONE II. The anatomic ankle implant design produced smaller contact stress with no evident edge contact and a smaller tibia-implant interface micromotion. In addition, significant differences in the magnitudes and tendencies of total ankle contact forces and motions among different patients were found. ConclusionsThe articular surface geometry of ankle implants not only affected the ankle motions and contact stress distribution but also affected the bone-implant interface micromotions. The anatomic ankle implant had good performance in recovering ankle joint motion, equalizing contact stress, and reducing bone-implant interface micromotion. INFINITY's fixation design could achieve smaller bone-implant interface micromotion than INBONE II.

A novel asymptotic formulation for partial slip half-plane frictional contact problems

A method of solution and the necessary calibrations are given to permit the steady-state extent of slip to be found in contacts properly described within a half-plane formulation using only two parameters: the contact law and the first-order descriptions of tractions arising at the contact edges. The approach takes the assumption of full stick and corrects for the slip regions using an array of glide dislocations. This is a very versatile approach and is particularly appropriate when studying fretting fatigue, as it permits the region in which cracks nucleate to be defined very simply, and in a form which is transportable from contact to contact, including laboratory tests. The approach has the additional benefit of giving a relatively straightforward expression for the density of dislocations, from which the slip displacement and shear traction within the stick region may readily be calculated. An example implementation is provided in the case of a Hertzian contact in the absence of changes in bulk tension, for which we demonstrate the veracity of the predictions by comparing to previous asymptotic approaches that build upon the traction solution under the assumption of full sliding, as well as the known exact solution.

The adhesion of viscoelastic bodies with slightly wave surfaces

Adhesive contact of viscoelastic bodies is a challenging problem due to its rate-dependent nature. In this work, we formulate a theoretical model to describe the pulling process of a slightly wavy indenter from a soft medium, comparing predictions with numerical simulations. A cohesive approach is adopted to formulate the theory based on the assumption that viscoelastic dissipation is confined to a small region around the contact edge. The resulting increase in surface energy is related to the quasi-static work of adhesion through the creep compliance. Theoretical findings match quite good numerical results. However, when separation arises from complete contact, the pull-off force can be estimated only if a small flaw is postulated at the interface.

Modeling the hydrodynamic impact on the tool influence function during hemispherical subaperture optical polishing

To fabricate high-precision and accurate optics relative to the optical design surface, a high level of deterministic control of material removal (i.e., the tool influence function, TIF) during subaperture tool polishing is required. In this study, a detailed analysis of the pressure distribution, which is a key component of the TIF, has been performed using finite element analysis to couple together solid mechanics and fluid dynamics. Modeling experimental parameters of recently published work reveals that, when considering tool deformation, which in turn influences the fluid film thickness between the tool and workpiece, the effective pressure profile has a flat-top distribution. This flat-top pressure profile differs from the parabolic pressure distributions predicted by Hertzian mechanics. Moreover, the shear contribution is shown here to be a key contributor to material removal, inducing the removal at the periphery of the contact edge and even outside the generally accepted contact area. Finally, the simulated fluid velocities provide evidence of mixed-mode contact polishing, supporting recent experimental findings that also suggest that onset of hydroplaning contributions lead to material removal drop-off.

Ab initio simulations of metal contacts for graphene-based devices

The precise atomic structure of a metal contact significantly affects the performance of nanoscale electronic devices. We use an accurate, DFT-based non-equilibrium Green’s function method to evaluate various metal contacts with graphene or graphene nanoribbons. For surface metal contacts not chemically bound to graphene, Ti contacts have lower resistance than those of Au, Ca, Ir, Pt, and Sr. However, as an edge contact, Ti has larger resistance than Au. Bridging O atoms at Ti and Au edge contacts lowers the transmission by over 30%.

WO3 Passivation of Access Regions in Diamond MOSFETs

We study the impact of access region passivation on the electrical characteristics of hydrogen-terminated diamond MOSFETs with tungsten Carbide (WC) edge contacts. Our experiments reveal a significant improvement to both contact and extrinsic channel sheet resistance once the access regions are passivated with WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , indicating that WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is an effective surface transfer-doping agent. We analyze a peculiar bump that appears in the subthreshold characteristics of the devices that prevents their effective turn-off. The bump is found to be mitigated when the access regions are passivated by WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . Poisson–Schrödinger (P–S) simulations suggest that this bump arises from the field-effect action by the gate over the access region immediately adjoining the gate. This parasitic field effect arises when the surface is unpinned and with a light hole concentration. Owing to its increased surface transfer doping, the use of WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as surface passivation is effective in delivering a sharp device turn-off.

Meshing Simulation of Face-Gear Drives using Multibody Dynamics Software

This paper aims to conduct the meshing simulation of two designs of face-gear drives (FGDs) by using the multibody dynamics software, SolidWorks motion. The pinion in the original design of FGD is not provided with any crowning modification, but the pinion in the improved design of FGD is provided with both profile and longitudinal crowning modifications. The results obtained by the meshing simulation show that the edge contact phenomenon greatly reduces the transmission stability of the original design. By giving the pinion a convex dressing in two directions, the transmission stability can be largely improved. The fluctuation in angular velocity and angular acceleration of the improved design of FGD is obviously lower than those of the original design.